EP No. 221 776A (Unilever), published on May 13, 1987, describes and claims novel porous materials suitable for carrying liquid components in detergent compositions. One such material, crystal-growth-modified Burkeite, is prepared by drying (preferably spray-drying) a slurry containing sodium carbonate and sodium sulphate in an appropriate ratio and a crystal growth modifier, added to the slurry not later than the sodium carbonate so as to influence the growth of crystals of the double salt Burkeite. Crystal-growth-modified Burkeite is characterised by a high capacity for taking up liquid detergent components and one possible way in which it may be used in detergent compositions is as a base or carrier for nonionic surfactant in an "adjunct" which is postdosed to a spray-dried base powder. The adjunct is prepared by spraying liquid or liquefied nonionic surfactant onto the modified Burkeite carrier material, and is then postdosed to a spray-dried base powder containing anionic surfactant, possibly nonionic surfactant, phosphate and/or non-phosphate builder, sodium silicate, fluorescer and other non-heat-sensitive ingredients: this procedure is especially beneficial as a method for incorporating in powders those nonionic surfactants that are unsuitable for spray-drying because of unacceptable tower emission ("pluming" or "blue smoke"). The adjunct may, for example, contain from 5 to 40% by weight of nonionic surfactant, and may itself constitute, for example, from 5 to 20% by weight of the final detergent powder.
Phosphate-built and zero-phosphate powders containing such adjuncts are described in the aforementioned European specification in Examples 24 and 25: in comparison with similar powders where the nonionic surfactant was incorporated via the slurry, both powders exhibited substantially improved physical properties. To prepare these powders, however, two separate spray-drying operations--of the Burkeite carrier, and of the base powder--are necessary. This can cause difficulties in factories having only one spray-drying tower, and may necessitate storage of the Burkeite carrier material on site for prolonged periods and/or transport of this material between different factory sites.
It has now been discovered that powders of comparable properties can be prepared in a single spray-drying tower by spraying in separate slurries of powder and crystal-growth-modified Burkeite to form a composite product, and subsequently spraying liquid nonionic surfactant onto the composite product. The process can be used also for other porous carbonate-based carrier salts and other liquid detergent components.